1. Field of the Invention
The present invention relates to a thermoplastic resin composition which is excellent in rigidity, impact resistance and fluidity and from which molded articles having excellent appearance, particularly having favorable flow marks, can be obtained. In addition, the present invention relates to an injection-molded article comprising the thermoplastic resin composition.
2. Description of the Related Art
Polypropylene-based resins have been used widely in materials which are required to have, for example, high rigidity and high impact strength. Polypropylene-based resins have recently been used widely especially as materials for automobiles. In particular, ethylene-propylene block copolymers are used increasingly. Although ethylene-propylene block copolymers have conventionally been produced by a solvent method, such copolymers have recently been produced by a continuous gas phase method which comprises a simple production process and by which those copolymers can be produced at low cost.
However, an ethylene-propylene block copolymer produced by the gas phase method contains an ethylene-propylene copolymer portion having a low intrinsic viscosity [η]EP. Therefore, the block copolymer generally has problems that it has a low swelling ratio (SR), that it forms unfavorable flow marks and that molded articles produced therefrom have poor appearance. Moreover, when an ethylene-propylene block copolymer is used which was produced by the gas phase method and which has a high intrinsic viscosity [η]EP, pimples are formed therein and molded articles having poor appearance are obtained therefrom.
For solving the appearance problems mentioned above, JP-A-07-286022, for example, discloses a propylene-based block copolymer produced by a batchwise solvent method. The block copolymer contains a n-decane(23° C.)-insoluble component having an intrinsic viscosity of 0.1 to 20 dl/g and a n-decane(23° C.)-soluble component having an intrinsic viscosity of 5 to 15 dl/g. From the block copolymer, molded articles free of pimples can be formed. However, as disclosed in Comparative Example 3 in the foregoing document, an ethylene-propylene block copolymer containing a n-decane(23° C.)-soluble component of a high intrinsic viscosity, which component seems to be an ethylene-propylene block copolymer portion, contains many rubber granules which will cause pimples.
JP-A-07-286075 discloses a propylene polymer composition comprising a propylene polymer produced in a continuous mode and an ethylene-propylene block copolymer containing a n-decane(23° C.)-soluble component having an intrinsic viscosity of 5 to 12 dl/g. This document discloses that molded articles free of pimples can be formed from the composition. However, the content of the ethylene-propylene block copolymer compounded is as much as at least 12% by weight.